The complete, or partial, detachment of ligaments, tendons or other soft tissues from their associated bones within the body is a relatively commonplace injury, particularly among athletes. Such injuries generally result from excessive stresses being placed on these soft tissues. For example, a tissue-detaching injury may occur as the result of an accident such as a fall, overexertion during a work-related activity, during the course of an athletic event, or in any one of many other situations and/or activities.
In the case of a partial detachment, commonly referred to under the general term "sprain" the injury will frequently heal itself, if given sufficient time, and if care is taken not to expose the injury to any undue or extraordinary stress during the healing process. If, however, the ligament or tendon is completely detached from its associated bone or bones, or if it is severed as the result of a traumatic injury, partial or permanent disability may result. Fortunately, a number of surgical techniques exist for re-attaching such detached tissues and/or completely replacing severely damaged tissues.
One such technique involves the re-attachment of the detached tissue using "traditional" attachment devices such as metal staples, sutures over buttons and cancellous bone screws. Such "traditional" attachment devices have also been used to attach tendon or ligament substitutes (often formed of autogenous tissue harvested from elsewhere in the body) to the desired bone or bones.
Another technique is described in detail in U.S. Pat. No. 4,950,270 entitled "Cannulated Self-Tapping Bone Screw", issued Aug. 21, 1990 to Bowman et al. This patent is specifically incorporated herein by reference. In this technique, an anterior cruciate ligament in a human knee, for example, is replaced and/or repaired by forming bone tunnels through the tibia and/or femur at the points of normal attachment of the anterior cruciate ligament. A ligament graft, with a bone block (or plug) on at least one of its ends, is sized to fit within the bone tunnels. Suture is then attached to the outer end of each bone plug, and thereafter passed through the femoral and/or tibial bone tunnels. The femoral plug and/or the tibial plug is/are then inserted into the appropriate bone tunnel behind the suture. Subsequently, the suture is drawn tight (simultaneously in opposite directions, in cases where bone blocks are to be located in both a femoral bone tunnel and a tibial bone tunnel). This procedure positions the bone plug (or plugs) in the desired location, and imparts the desired degree of tension to the ligament or ligament substitute. Finally, while holding the bone blocks in position, a bone screw is inserted between each bone block and the side wall of its associated bone tunnel so as to securely lock the bone block in position using a tight interference fit.
Alternatives to the foregoing use of bone screws are also well known in the art. For example, in U.S. Pat. No. 5,147,362 entitled "Endosteal Ligament Fixation Device", issued Sep. 15, 1992 to E. Marlowe Goble, rearwardly extending flexible barbs or pins are attached to a bone plug (either directly or by a collar, cap or similar intervening element) for anchoring a bone plug within a bone tunnel. The disclosure of the foregoing U.S. Pat. No. 5,147,362 is specifically incorporated herein by reference.
In U.S. Pat. No. 4,997,433 entitled "Endosteal Fixation Stud and System", issued Mar. 5, 1991 to E. Marlowe Goble et al., a stud is disclosed for attachment to the outer end of the bone block. This stud includes a pair of spaced, forwardly projecting, flexible arms. One of these arms includes a substantially rigid, radially and rearwardly projecting portion disposed adjacent the arm's outer end. The stud is inserted through a bone tunnel ahead of a bone block to which it has been attached so that the projection may engage the outer surface of the bone adjacent the far end of the bone tunnel. This projection then acts to hold the bone block within the bone tunnel so long as rearwardly directed tension is maintained on the bone block. The disclosure of U.S. Pat. No. 4,997,433 is also specifically incorporated herein by reference.
Unfortunately, the repair devices and methods described above have not been uniformly successful. For example, tissue re-attachments effected using the aforementioned "traditional" fastening devices often cannot be maintained under even normal tensile loads.
Also, the use of sharp screws to create a locking interference fit between a bone plug and the side wall of a bone tunnel introduces a number of problems. For one thing, there is always the possibility of damaging the ligament or repair material during insertion of the sharp screw. In addition, it can be difficult to maintain the desired tension on the ligament or repair material during insertion of the screw. Furthermore, the insertion of a bone screw requires that a twisting motion to be imparted to the screw. This twisting motion of the screw can in turn cause rotation of the bone block within the bone tunnel. If this occurs, undesirable twisting of the ligament may also occur.
The removal of such bone screws can also cause problems. In those cases in which the screw can be removed simply by unscrewing it in the usual manner, an undesirable hole is left in the bone. In many cases, however, the screw cannot simply be unscrewed from the bone to remove it. In these situations, the screw must typically be either forceably pulled out of the bone, or it must be removed by chipping away the surrounding bone. Both of these removal procedures can cause serious damage to the bone.
The foregoing attachment devices of U.S. Pat. Nos. 5,147,362 and 4,997,433 are also not totally satisfactory. This is because in the device of U.S. Pat. No. 5,147,362, the cross-sectional size of the bone tunnel must significantly exceed the cross-sectional size of the bone block due to the particular constructions utilized. This results in the bone block being spaced from the side wall of the bone tunnel, which can in turn delay assimilation of the bone block into the bone during healing. The device of U.S. Pat. No. 4,997,433, on the other hand, is limited to use in a particular method of re-attachment. Furthermore, undesirable binding may occur between the stud's projection and the side wall of the bone tunnel as the stud is forced through the bone tunnel.
Various types of suture anchors and anchors for attaching objects to bone are also well known in the art. A number of these devices are described in detail in U.S. Pat. Nos. 4,898,156; 4,899,743; 4,946,468; 4,968,315; 5,002,550; 5,046,513; and 5,192,303 (each of which is presently owned by Mitek Surgical Products, Inc. of Norwood, Mass., the assignee of this application). The disclosures of these patents are also specifically incorporated herein by reference.